The Roman Gold Mine that Ate Mountains

Here at Las Medulas, in the rugged northwest of Spain, a mountain is missing. It vanished 2,000 years ago when miners, channeling the water of six aqueducts, washed it away to expose the gold that financed the power of Rome. Today's video will survey how this incredible operation worked and explore the strange landscape left behind by the ancient miners. From the reign of Augustus to the final days of Byzantium, the Roman Empire ran on gold. Soldiers and officials were paid in gold coins. So was the tribute demanded by Attilo the Hun. Gilded busts of the emperors were carried in processions, and empresses appeared before the people in gowns of gilded cloth. This gold came from many sources. Caesar seized so much from the sanctuaries of Gaul that the value of precious metal dropped throughout Italy. Hundreds of tons, hidden on the orders of the Dacian king Decebalus, were reportedly recovered from a river in Transylvania. Mines were scattered throughout the provinces. Those of Mount Pangaeon, which had once underwritten the rise of Alexander the Great, were especially famous. The most productive mines, however, were in Spain. Pliny the Elder describes a mine that cut a mile and a half into the mountains and was so deep that it had to be continuously pumped by slaves working waterwheels. The open-cast mines of northwestern Spain were on an even grander scale. Here, as throughout the empire, gold mines were owned by the state and overseen by an imperial procurator. Individual mines were managed by imperial freedmen who leased concessions to private contractors. Although these contractors employed both slave and free workers, the most dangerous work was always done by condemned prisoners. There was plenty of dangerous work at Las Medulas, the most spectacular of Roman Spain's gold mines. The site began to be exploited early in the first century A.D., not long after Augustus added the surrounding region to the empire. Over the next 150 years, a workforce that may have sometimes swelled to 20,000 men transformed what had been a nondescript valley into a moonscape. The gold of Las Medulas was embedded in layers of sand and clay that had eroded from the Sumiedo Mountains. Only some strata contained gold, and these were buried beneath up to a hundred meters of sterile sediment. Where the gold-bearing strata were close to the surface, water was funneled through networks of converging trenches and into a central channel where miners strained suspended gold flakes from the stream, a process analogous to the hydraulic mining used to such devastating effect in the later stages of the California gold rush. Where the gold was deeper, the Romans resorted to the method that Pliny described as ruina montium, the ruin of mountains. More on that after the break. Like many history enthusiasts, I spent years trying to find shirts that matched my passion. Not toga silhouettes from a gift shop or some misquotation of Cicero. I wanted something with real thought behind it. Today's sponsor, Echoes of Antiquity, provides exactly that. With more than a thousand designs ranging over antiquity, the medieval world, and literary culture, Echoes of Antiquity has a shirt for just about anything you are likely to be reading about. Each design is built around a specific reference. This one, for example, shows the Morton Salt Girl with Cato the Elder's famous warning, Carthage must be destroyed. A fun allusion to the proverbial salting of Carthage. Follow the link in the description and find a shirt that suits your interests. Save 20% with the code TOLDONSTONE20. Returning to our topic. What Pliny called ruina montium is now known as hushing. A network of galleries was cut into the sediment covering the gold-bearing strata. The work, Pliny tells us, could take months. When the miners encountered masses of rock too hard for their picks, they cracked the stones with fires, or 150-pound weights. Once the tunnels were finished, they were flooded. To obtain the vast amount of water required, the miners built aqueducts through the mountains. Pliny describes the immense labor of driving conduits through ridges and over valleys. In some places, the channels were supported on precarious wooden trestles. In others, they had to be carved from sheer cliff bases by men suspended from ropes. The aqueducts that served Las Medulas eventually included about 600 kilometers of water channels, which supplied between 50 and 90 million cubic meters of water annually. Much of this was held in reservoirs above the mines. When the hushing galleries were ready, the reservoir's stone sluice gates were opened. The force of the water thundering through the tunnels and saturation of the surrounding sediment created landslides that stripped away millions of tons of overburden. The miners at Las Medulas used the ruina montium technique again and again, creating a caldera that covered more than 10 square kilometers, by far the largest open-cast mine in the Roman Empire. Once the gold-bearing strata had been exposed, the miners piled the larger stones into heaps and dug channels along the surface. They lined the bottoms of the channels with gorse branches, then played streams of aqueduct water over the slopes. Gold flakes were washed downhill and caught in the gorse. They were retrieved after the branches were dried and burned. More than a hundred million cubic meters of sediment were washed down from the mines at Las Medulas. The debris transformed the topography of the plain below, leaving a series of ridges and channels. In channels blocked by later floods, lakes formed. Some, like Lake Sumido, are still extant today. The gold-bearing strata at Las Medulas were not especially rich. By one estimate, they carried only about three grams of gold for every ton of sediment. Around the beginning of the third century, the sheer difficulty of recovering gold from the site seems to have brought mining to an end. Since the mines were never reopened, Las Medulas remains largely, as the Romans left it, a monument to both the scale and the limitations of ancient ingenuity. To see more monuments of ancient ingenuity, join me next spring in Tunisia, where we'll be exploring the ruins of Carthage, Duga, and many other fascinating sites. I'm also leading a tour to Jordan, which will include the colonnaded streets of Jerash, Roman forts and crusader castles, and the wonders of Petra. You'll find links for both tours in the description. My new book, Leaky Aqueducts, Battle Pigeons, and Mystery Cults, is now available wherever books are sold. There's an Amazon link below. Finally, please check out the Toldonstone Patreon, where I'm reviewing HBO's hit series, Rome, and my other two channels, Toldonstone Footnotes and Scenic Routes to the Past. Thanks for watching!